Reporter: Already victorious over leukemia, miles scott lived out his fantasy, alongside batman himself. In order to transform the city by the bay, into a fantasy land. Thousands of citizens chipped in. From ordinary citizens, to the chief of police. Caped crusader, we need you. And bring the batkid. Reporter: Batkid and batman burst on the scene, to save a damsel in distress. The pint-sized wonder freed her, with thousands of adoring fans chanting his praises. That was just the beginning of his action-packed day. Dealing out bat justice to a truly gotham-worthy crime spree. After napping the riddler in the middle of a bank heist, the superhero stopped for a bat bite. Batkid is having lunch right now. But there's no rest for him. We're hearing reports that a penguin has kidnapped the mascot of the san francisco giants. A flash mop alerted the batkid. While the penguin roused about the flap he caused. Do you think you can take him? Oh, yeah. Reporter: Wrong again, bird brain. The dynamic duo gave chase. And while the bat nailed the crook, his counterpart freed the seal. For all of his hard work, batkid got a key to the city. Cheered on by a city inspired by his very real bravery all along. He never lost heart. He was always upbeat. He's our hero. Reporter: All of it thanks to the make-a-wish foundation. There's been plenty of superheros that make-a-wish has had. Nothing like this has happened. This is beyond our expectations. It's crazy. Reporter: For "good morning america," aditi roy, abc news, gotham city. That's such an amazing city. Amazing city. And the fact we love san francisco anyway. But to see it's beautiful inside and out. And the people coming together. What do you get him for christmas now?

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